Apparatus in the form of windmills and the like are well known for harvesting wind energy and converting it into more useful forms such as mechanical or electrical energy.
Modern windmill devices have developed into fairly complex pieces of equipment that are expensive to assemble and maintain. The present invention provides a wind impeller that is of very simple yet rugged construction that automatically exposes a large surface area when moving with the wind and a small surface area when moving against the wind to maximize the driving force of the wind.